Does premium gas

[gwl123]

make a difference? My first month of ownership on my '76 911 is mixed. I pumped regular gas in my car and it and now it won't start right. I thought it was the battery but not sure (will check the maint. records). After spending 30 mins on the intersection it finally started. Made it home luckily but I don't trust the car now.

[dlagerstrom]

It all depends on your compression ratio.

High compression ratio needs high octane so as not to pre-detonate.

Using a lower octane fuel shouldn't have anything to do with getting the car started as I understand it. I think you have some other issues.

What were the other symptoms of 'not starting'?

[defcon65]

Assuming the engine is stock, you should use whatever the manual specifies. My '85 Carrera will run just fine on 87 octane. I have pumped 93.5 before and couldn't tell the difference in either power or mileage. I do get slightly lower mileage with the 10% ethanol fuels that are so common anymore.
Sounds to me like your problem is more mechanical in nature. I'd check the basics - filters, plugs, hoses, pump, dist cap and rotor, wires - all the tune-up stuff. Good luck.

[Rot 911]

Octane of gas doesn't have anything to do with a start/no start condition.

[roadhog]

+1 to all the above , regular ignites easier thats why it detonates prematurely .It can be set off by hot spark plug tips.Some low comp. antique engines can,t run on modern gas because the octane is too high.

[JV911SYDNEY]

Originally posted by defcon65

Sounds to me like your problem is more mechanical in nature. I'd check the basics - filters, plugs, hoses, pump, dist cap and rotor, wires - all the tune-up stuff. Good luck.

+1

Our "regular" fuel in Aus is 92 and high octane is 98

I run 98 octane. just replaced plugs, dizzy cap, etc etc etc and car runs like a dream

[stlrj]

Your 76 911 engine is designed for regular so why not find a better way to waste your money.

[Bill Douglas]

Hi octane fuel doesn't have more "balls", it's just ordinary fuel with additives to make it not ignite so easily.

[SC-targa]

Octane shouldn't impact starting on a 911.

Originally posted by roadhog


+1 to all the above , regular ignites easier thats why it detonates prematurely .It can be set off by hot spark plug tips.Some low comp. antique engines can,t run on modern gas because the octane is too high.

I drove thousands of miles on my 1923 Packard and my dad's old 1920 Mitchell running regular unbleaded and never had any problems that were fuel related. The Packard had a 4 1/2:1 compression ratio.

How much lower do you think any other antique engine's compression ratios were?

Mine was designed for fuel with an octane rating of 25 to 30, (before tetra ethyl lead was introduced) if I recall correctly.

Regards,

Jerry Kroeger

[M.D. Holloway]

I studied this years ago with an 86 Camry. I actually logged the miles driven and the money sent comparing 93 and 89 for an entire year. On the average, I got an extra 4 mpg more with the 93 but the price difference made it a perfect wash. I did not do a performance study - only mpg.

[dfink]

I may be wrong but would a car with knock sensors take advantage of the higher octane by advancing the timing and possibly getting better performance and mileage. Just a thought. One thing about premium in many places is an ethanol blend. The octane is higher but the energy output is lower unless the car is modified. In Nebraska we have both ethanol enhanced premium sometimes called super and the non-alcohol premium. Usually the cheap places have the ethanol and places like BP have the real premium fuel.

[nineoneone]

try this and you can't go wrong....

Pull the relay under your seat for the fuel pump,
pull it apart..i.e. pull the contact section out so you can look at it.
look in the bottom of the plastic cover and fold a match book cover once, not the whole thing but a piece about the size of the square cover 1"X1" or so, fold it over once place in bottom of plastic cover and install the relay again, you will note that the circuit board is not centered so try to make sure that the paper is in a position to fold as you slide it in. think of it like this


the V is the paper, dashes are the circuit board with the offset toward the bottom of the V

V---]

hope this helped, after fuel pumps and relay replacement and being stranded a few times. I worked with my old relay and got it to work this way. still to this day it works.

[RoninLB]

i get about 1-1.5 better millege w/reg. Less additives = more fuel.

i don't recommend reg.

[FenderGuy]

So your saying my 80 SC could run on 87 instead of 91? I just put the Prem gas thinking it was better for the car

[emac]

Frank
I would stick with the Prem. With all the noise back there we wouldn't hear the pre. ign.

[Tim Hancock]

Nothing but 87 in my '79 SC. I think it has lower compression than the later SC's though.

[FenderGuy]

Prem is it is then and you are right noisy but fun

[stlrj]

So your saying my 80 SC could run on 87 instead of 91?

Even your owners manual specs regular.

[JV911SYDNEY]

Originally posted by stlrj
Your 76 911 engine is designed for regular so why not find a better way to waste your money.

1. 76 was designed for leaded which you cant get anymore. mechanics and friends have recommended high octane unleaded to prevent pinging.

2. i think i can affort the whole $2 extra it cost to fill a tank with premium.

[Paulporsche]

We need more info from you on symptoms regarding your no start condition. The octane rating most likely has no bearing on this.

I have to disagree w/ the previous comment on leaded fuel. 911 engines don't require the properties of lead like many others of that era did. The octane rating is just achieved using other materials today.Your 2.7 if stock should do OK on the specified octane, provided you haven't changed the compression, timing, etc. Having said that, older engines sometimes require a little extra octane level due to factors like engine wear and carbon buildup. If you want to be sure, go from 87 to 89, but there's no reason to go higher.